236 



THE CEPHALOPHORA. 



§210. 



The posterior plexus is composed of a single mass, rarely of two separate 

 ganglia. It is situated under the digestive canal or between its coils, and 

 from it pass off nerves to the intestine, the liver, and the genital glands, 

 beside two cords of communication with the lower portion of the oesophageal 

 ring.*^' 



CHAPTER IV. 



ORGANS OF SENSE. 



§ 210. 



The Tactile organs of the Cephalophora consist of two to four contractile 

 tentacles situated upon the hend, or the anterior part of the back.'" They 

 receive nerves of considerable size from the cerebral mass, which have some- 

 times a ganglionic enlargement in the extremity of the tentacle.*-' With 

 some Gasteropoda these tentacles are hollow and button-like at their ex- 

 tremity, and can be inverted like the finger of a glove. *^' But with the 



sia, p. 23, PI. r\'. fig. 1, c. ; sur la Lyinnee, p. 

 9, PI. I. fijc. 11, u. ; sur I'Onohidie, p. 14, PI. I. 

 fig. 6, o. Brandt (.Med. Zool. II. p. 328, Tab. 

 XXXIV. fig. 11, 13) has described it with Helix 

 pomatia ; Van Beneden (loc. cit.), with Amplii- 

 peplea, and Treviranus (Beubacht. aus. d. Zoot. 

 und Pliysioi: p. 42, Taf. IX. fig. 60), with Umax. 

 See also the researches of Schlemm (Dissert, de lie- 

 pate ac bile crustacecirum et moUuscorura quorun- 

 dam, Berol. 1844, p. 22, Tab. I. fig. 2, 3), upon the 

 hepatic nerves of Gasteropoda. Delle CA;o;> also, 

 has seen this plexus with Doridium and Pleuro- 

 branckus (Memor. II. p. 123, Tav. X. fig. 7, p. 

 and III. p. 153, Tav. XLl. fig. 8, p.). According 

 to Garner (loc. cit.), there is a double Ganglion 

 pharyngeum inferius with, also, Scyllaea, Doris, 

 and Eotis. With Patella, on the contrary, he 

 found this anterior Plexus splanchnicus composed 

 of three ganglia, two upon the sides, and the third 

 median and a little behind. 



According to Van Beneden (Exercices zoot. 

 Fasc. I. p. 30, PI. I. fig. 12, c), there is a similar 

 disposition with Amphipeplea. With the Iletero- 

 poda, this plexus is highly developed, composed of 

 two ganglia, from which pass off long cords of com- 

 munication to the cerebral mass ; see Milne Ed- 

 wards, Ann. d. Sc. Nat. XVIII. p. 327, PI. XI. 

 fig. 1, s. X. and fig. 2. e. f. ; and Delle Chiaje, 

 Descriz. &c. loc. cit. Tav. LXIII. fig 14, 1. and 

 LXIV. fig. 11, d. {Carinaria and Pterotrached). 

 The Pteropoda also have this plexus ; but its two 

 ganglia are more or less intimately fused, and as 

 the cerebral mass is here replaced by a simjfle col- 

 lar, it does not connect with it, but with the infe- 

 rior portion of the «esoi)hageal ring ; see Van Be- 

 neden, Exercices zoot. Fasc. II. ]). 11, et seq. PI. I. 

 fig. 9, 10, II. fig. 8, 10, III. fig. 6, 9, and V. fig. 



* [§209, note 2.] For the splanchnic nervous 

 system of the terrestrial Gasteropoda, see Lcidy, 

 loc. cit. PI. XIII. fig. IV. 2 {Helicina), PI. XIV. 

 fig. IV. 3 (Glandina), and PI. XVI. fig. II. 2 

 (Helix). 



See also for. that of the Nudibranchia, Aldrr 



13 (Ci/mbulia, Tiedemannia, Hyalea and Limn- 

 cina.) * 



3 The Plexus splanchnicus posterior with its 

 two long cords of communication is quite apparent 

 with Aplysia (see Cuvier, loc. cit. p. 23, PI. IV. 

 fig. 1, K.). Delle Chiaje (Memor. Tav. V. fig. 1, 

 m, X. fig. 7, o. and XLI. fig. 8, y. y.), has observed 

 it with Doridium, and Pleurobranchus, be- 

 side the genus just mentioned , and in Pleuro- 

 branchus, he found it composed of two entirely 

 separated ganglia. Van Beneden (Exerc. zoot. 

 Fasc. I. p. 46, PI. I. fig. 3-5) has found it com- 

 posed of only a single ganglion with Pneiimoder- 

 mon. Milne Edwards (loc. cit. p. 329, PI. XI. 

 fig. 1, u. v. 6), has observed in the visceral sac of 

 Carinaria, first, a double Ganglion ahdominale, 

 which receives two long cords of communication 

 from the cerebral mass and from the Ganglion 

 pedale, and then a Ganglion anale, communi- 

 cating with the two abdominal ganglia. 



1 There are most usually two tentacles. But with 

 Limax, Arion, Helix, Achatina, Clausilia, and 

 other Helicina, there are four. They are wholly 

 wanting with Sagitta, Cleodora, Cnvieria, Hya- 

 lea, Pterolrachea, Lissosoma, Rhodope, Phyl- 

 lidia, and Dentalium. 



'^ This swelling exists not only with the inferi- 

 or and eyeless tentacles, but also the superior ones 

 bearing eyes, with several Limacina and Helicina. 

 However, no ganglionic globules are seen in it, and 

 only a finely-granular substance lies interposed be- 

 tween the primitive fibres. 



3 With the Limacina and Helicina, these organs 

 are invested by a muscle which arises upon the 

 columnflla or upon the internal surface of the 

 mantle, and is inserted at the e.xtremity of each 

 tentacle. 



and Hancock, loc. cit. (Eolis, Doris, Antio- 

 pa, &c.). 



According to Middendorff (loc. cit. p. 76), Chi- 

 ton has a complex splanchnic nervous systeia 

 which is widely distributed over the digestive or- 

 gans and their auxiliary glands. — Ed. 



